1. Field of the Invention
The present invention relates generally to fluid flow control valves and more particularly to an improved valve assembly and having leak detection means and provisions for leak containment.
2. Brief Description of the Prior Art
There are numerous fluid flow control applications in which corrosive, caustic or chemically pure liquid flows must be controlled and various attempts have heretofore been made to provide suitable pneumatic and electrically actuated valves suited for such purpose. One such valve is the subject of De Lorenzo et al. U.S. Pat. No. 4,010,769. which discloses a valve including a plunger that is moveable by actuating means such as a solenoid, air valve or other means to move a closure member toward and away from a valve seat. The fluid handling position of the valve is sealed from the actuating means by secondary diaphragms, 0-rings or other forms of sealing structures in order to insure against leakage past the primary diaphragm or seal and especially against leakage into the actuating means. In the event of leakage past the first sealing means, flow of the liquid into the space between the first and second sealing means causes an outward flow of fluid through a venting passage which thereby provides an indication of leakage past the first sealing means so that the leak will be noticed and the first sealing means can be replaced before any damage to the actuating means or to the system itself occurs.
Although this valve is suitable for enabling detection of diaphragm failure, it is not directed toward applications in which corrosion or contamination of either the actuator mechanism or the fluid itself must be strictly limited. For example, in the semiconductor manufacturing industry the processing chemicals and deionized water supplies must be kept as pure as possible since even a momentary contact of the flow stream with a contaminating surface can result in a catastrophic event. Although the valve closure member shown in FIG. 1 of De Lorenzo is indicated as being made of Teflon, the surrounding valve body and associated parts appear to be metallic and would thus not be suited for applications in which diaphragm failure is likely to cause almost immediate contamination of the controlled fluid. Moreover, the thrust of the De Lorenzo invention is to protect the actuating mechanism from unintentional exposure to the controlled fluid as opposed to being directed to preventing contamination of the fluid. Futhermore, the valve device per se is a gate valve of a type which is not suited for certain applications in which back flow pressures can unseat the gate or perhaps even prevent its closure. And finally, no means for automatically detecting diaphragm failure is provided.
Another problem associated with valves of the type disclosed by De Lorenzo, et al. is that frictional engagement of sealing surfaces deleteriously affects the useful lifetime of the valve, and the tendency of the sealing surfaces to be residually deformed after closure for extended periods of time may limit the sealing ability of the device. The Stack U.S. Pat. Nos. to Stack 4,538,638, Botelar 3,407,838, McFarland 3,542,286 and Priese 3,451,423 disclose weir type valves are more suited to such applications. However, such devices have not been adapted to address the problem of fluid contamination as a result of the leakage and the need for immediate and automatic detection of diaphraqm failure.
SUMMARY OF THE PRESENT INVENTION
It is therefore a principal objective of the present invention to provide an improved fluid flow control system having means for avoiding contamination of the controlled fluid in the event of valve failure.
A further object of the present invention is to provide a device of the type described which includes means for providing immediate detection of diaphragm failure.
Another object of the present invention is to provide a device of the type described having leak containment features.
A still further object of the present invention is to provide a device of the type described having sealing surfaces which mate without substantial rubbing contact.
Briefly, a preferred embodiment of the present invention comprises a fluid handling system incorporating one or more flow controlling devices including an actuator, a weir valve and associated valve housing, a pair of spaced apart diaphragms, one of which serves as the closure member for the weir valve and the other providing a secondary seal defining the limits of a containment chamber for at once preventing contamination of the controlled fluid, protecting the actuating mechanism and allowing immediate detection of the valve closure failure. A piston member disposed within the chamber is coupled to the two diaphragms, and a fluid detection device is disposed in communication with the sealed containment chamber formed between the two diaphragms. The system includes electronic control apparatus responsive to the detection device and operation to instantaneously shut down the system in the event of a detected failure.
An important advantage of the present invention is that even in the event of a diaphragm failure, no contamination will occur because all wetted surfaces of both valve and containment chamber components are constructed of or are coated with a chemically inert material.
Another advantaqe of the present invention is that in the event of diaphragm failure, diaphragm leakage will be contained within the space between the two diaphragms.
Yet another advantage of the present invention is that means is provided for immediately detecting diaphragm failure so that instantaneous shutdown of the fluid supply system can be achieved.
These and other objects and advantages of the present invention will no doubt become apparent to those skilled in the art after having read the following detailed description of the preferred embodiment which is described in the several figures of the drawing.